1. Field of the Invention
The present invention relates to a display device, and in particular, to a display device which scans an image display body such as a screen, a display panel or the like with a light beam modulated in accordance with an image signal and displays an image on the image display body.
2. Description of the Related Art
As conventional laser display devices, for example, devices (1)–(3) described below have been known.
(1) A device in which, one laser beam is modulated in accordance with image signal by a light modulation element, and this laser beam is deflected along a main scanning direction and a sub scanning direction, thereby, an image display body such as a display panel or the like is scanned with this laser beam and an image is displayed on the image display body.
(2) A device in which, laser beams are modulated in accordance with image signals by an one-dimensional spatial light modulation element in which a plurality of pixel portions are arranged in a line manner, and a set of the laser beams which are arranged in a line manner are deflected along a direction (a sub scanning direction) orthogonal to an arrangement direction (a main scanning direction), thereby, an image display body such as a screen or the like is scanned with this set of the laser beams and an image is displayed on the screen. (for example, refer a Japanese Patent Laid-Open No. 2000-131838)
(3) A device in which, laser beans are modulated in accordance with image signals by an two-dimensional spatial light modulation element in which a plurality of pixel portions are arranged in a two dimensional manner, thereby, a large number (a number of display-pixels) of the laser beams which are arranged in a two dimensional manner are image-formed on an image displayed body by respective image-forming systems and an image is displayed.
In the laser display devices mentioned above, generally, increasing of a number of display-pixels is necessary in order that a display image is made high definition. This will be described hereinafter concretely. For example, when considering in a case in which a monochrome image of pixels (10000×7500) is drawn (image-formed) in sixty frames per second. In a case of the laser display device (1) mentioned above, it is impossible as a matter of fact that the laser beam is modulated in accordance with the image signal by one light modulation element. Because a modulation frequency of the light modulation element is about 4.5 GHz, that is, it is very high speed (rate).
Further, in a case of the laser splay device (2) mentioned above, regarding a number of the pixels of the one-dimensional spatial light modulation element necessary to modulate the laser beams, at least 7500 pixels are necessary. On the other hand, it is general that a number of the pixels of the one-dimensional spatial light modulation element is about 1000 pixels at the most. Accordingly, in the case of the laser display device (2), many numbers of (more than or equal to eight) the one-dimensional spatial light modulation elements are necessary. In such a case, it is difficult to manufacture the device in low cost. Further, image quality deterioration (liner defect) caused by pixel defect of the one-dimensional spatial light modulation element may often occur.
Further, in a case of the last display device (3) mentioned above, at least 10000×7500 pixels are necessary regarding a number of the pixels of the two-dimensional spatial light modulation element necessary to modulate the laser beams. Therefore, in the case in which a plurality of the two-dimensional spatial light modulation elements are used to modulate the laser beams, problems which basically are the same as those in the case of the laser display device (2) arise. Further, in a case in which the two-dimensional spatial light modulation element whose number of pixels are 10000×7500 is manufactured, numerical quantity of devices (spatial light modulation elements) obtained from an one wafer becomes extremely small due to yield becoming low because of increasing of rate of occurrence of pixel defect and size of the device being large. As the result, the cost of the device becomes very high. Therefore, manufacturing cost of the laser display device using such the two-dimensional spatial light modulation element becomes also high.
Next, the result of studying a case in which animation (moving image) is displayed by the laser display device mentioned above will be explained. For example, in a case in which an image modulation period of an one image (frame) in a display device having a resolution of 10000 pixels in a sub scanning direction and 7500 pixels in a main scanning direction is calculated, a frame rate of at least 30 frames per second is required in order that flicker is not perceived and smooth animation is displayed. Normally, a frame rate of about 60 frames per second is required. Accordingly, in order to obtain frame rate of 60 frames per second, modulation period of a display image is “one second/30=16.7 ms”. Further in the case in which a resolution in a sub scanning direction is 10000 pixels, and assuming scanning efficiency of a scanning device such as a galvano mirror is 80%, modulation period per one pixel is “0.0167*0.8/10000=1.3 μs”. It is difficult to modulate pixel in accordance with image signal within such a short period by a general spatial light modulation element.